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| United States Patent |
6,130,379
|
|
Shiotsuka
, et al.
|
October 10, 2000
|
Protective material for a semiconductor element, a semiconductor element
provided with said protective material, and a semiconductor device
provided with said semiconductor element
Abstract
A highly reliable surface covering material for a semiconductor element or
a semiconductor device having a specific transparent resin layer formed of
a resin containing a silane coupling agent in a state with no free
material of said silane coupling agent. The element or device is free of
the occurrence of layer separation, has satisfactory heat resistance, is
hardly yellowed. The element semiconductor element or semiconductor device
effectively maintains its characteristics without deterioration, even when
repeatedly used over a long period of time under severe environmental
conditions with a high temperature and a high humidity.
| Inventors:
|
Shiotsuka; Hidenori (Tsuzuki-gun, JP);
Mori; Takahiro (Ikoma, JP);
Kataoka; Ichiro (Tsuzuki-gun, JP);
Yamada; Satoru (Tsuzuki-gun, JP);
Komori; Ayako (Nara, JP)
|
| Assignee:
|
Canon Kabushiki Kaisha (Tokyo, JP)
|
| Appl. No.:
|
680799 |
| Filed:
|
July 16, 1996 |
Foreign Application Priority Data
| Jul 19, 1995[JP] | 7-182954 |
| Jul 10, 1996[JP] | 8-181049 |
| Current U.S. Class: |
136/251; 136/259; 257/433; 257/790; 257/791 |
| Intern'l Class: |
H01L 031/048 |
| Field of Search: |
136/251,259
257/433,790-791
106/287.13
|
References Cited
U.S. Patent Documents
| 4729970 | Mar., 1988 | Nath et al. | 437/225.
|
| 5344498 | Sep., 1994 | Inoue | 136/251.
|
| 5344501 | Sep., 1994 | Hashimoto et al. | 136/259.
|
| 5482571 | Jan., 1996 | Yamada et al. | 136/259.
|
| 5530264 | Jun., 1996 | Kataoka et al. | 257/40.
|
Primary Examiner: Nguyen; Nam
Assistant Examiner: Miggins; Mike
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper & Scinto
Claims
What is claimed is:
1. A photoelectric conversion element having a light receiving face side
provided with a transparent and conductive layer, said light receiving
face side being covered by a transparent layer formed of a resin obtained
by crosslinking an acrylic resin and an inorganic polymer as a main
component, said resin containing an epoxy series silane coupling agent.
2. A semiconductor element according to claim 1, wherein the silane
coupling agent includes a compound represented by the general formula
XSiY.sub.3 with X being a reactive organic functional group and Y being a
hydrolyzable group.
3. A photoelectric conversion element according to claim 1, wherein the
resin as the transparent layer is crosslinked by an isocyanate.
4. A photoelectric conversion element according to claim 3, wherein the
isocyanate comprises one or both of hexamethylenediisocyanate or 1,3-bis
(isocyanatemethyl) cyclohexane.
5. A semiconductor element according to claim 3, wherein the isocynate has
an isocyanate group masked by .epsilon.-caprolactam.
6. A semiconductor element according to claim 1, wherein the epoxy series
silane coupling agent comprises at least one member selected from the
group consisting of
.gamma.-gylcidoxypropyltrimethoxysilane,
.gamma.-gylcidoxypropyltriethoxysilane, and
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.
7. A photoelectric conversion element according to claim 1, wherein the
transparent and conductive layer comprises an ITO film.
8. A solar cell module comprising (a) a photoelectric conversion element
having a light receiving face side provided with a transparent and
conductive layer, (b) a transparent layer formed of a resin obtained by
crosslinking an acrylic resin and an inorganic polymer as a main
constituent and which is disposed to cover said light receiving side of
said photoelectric conversion element, and (c) an organic resin layer
comprising a transparent thermoplastic polyolefin resin disposed to cover
said transparent layer (b), said transparent layer (b) containing an epoxy
series silane coupling agent.
9. A semiconductor device according to claim 8, wherein the silane coupling
agent includes a compound represented by the general formula XSiY.sub.3
with X being a reactive organic functional group and Y being a
hydrolyzable group.
10. A semiconductor device according to claim 9, wherein the X and Y of the
general formula XSiY.sub.3 are respectively a glicidoxypropynyl group and
an alkoxy group.
11. A solar cell module according to claim 8, wherein the resin as the
transparent layer is crosslinked by an isocyanate.
12. A solar cell module according to claim 11, wherein the isocyanate
comprises one or both of hexamethylenediisocyanate or 1,3-bis
(isocyanatemethyl) cyclohexane.
13. A semiconductor device according to claim 11, wherein the isocynate has
an isocyanate group masked by .epsilon.-caprolactam.
14. A semiconductor device according to claim 8, wherein the epoxy series
silane coupling agent comprises at least one member selected from the
group consisting of
.gamma.-gylcidoxypropyltrimethoxysilane,
.gamma.-gylcidoxypropyltriethoxysilane, and
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.
15. A solar cell module according to claim 8, wherein the transparent
thermoplastic polyolefin resin is a resin selected from the group
consisting of ethylene-vinyl acetate copolymer and ethylene-ethyl acrylate
copolymer.
16. A solar cell module according to claim 8, wherein the transparent layer
is a layer formed by means of a film-coating process.
17. A solar cell module according to claim 8, wherein the photoelectric
conversion element comprises a semiconductor active layer formed on an
electrically conductive substrate as a first electrode and the transparent
and conductive layer as a second electrode.
18. A semiconductor device according to claim 17, wherein the semiconductor
active layer comprises a non-single crystal semiconductor thin film.
19. A semiconductor device according to claim 17, wherein the non-single
crystal semiconductor thin film is composed of an amorphous silicon
material.
20. A solar cell module according to claim 8, wherein the transparent and
conductive layer comprises an ITO film.
21. A photoelectric conversion device comprising a photoelectric conversion
element having a light receiving surface, and a transparent layer provided
on said light receiving surface, wherein said transparent layer is derived
from a resin containing a silane coupling agent.
22. A photoelectric conversion device according to claim 21, wherein the
silane coupling agent includes a compound represented by the general
formula XSiY.sub.3, with X being a reactive organic functional group and Y
being a hydrolyzable group.
23. A photoelectric conversion device according to claim 21, wherein the
silane coupling agent includes an epoxy series silane coupling agent.
24. A photoelectric conversion device according to claim 23, wherein the
epoxy series silane coupling agent comprises at least one member selected
from the group consisting of
.gamma.-gylcidoxypropyltrimethoxysilane,
.gamma.-gylcidoxypropyltriethoxysilane, and
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.
25. A photoelectric conversion device according to claim 21, wherein the
resin is crosslinked by an isocyanate.
26. A photoelectric conversion device according to claim 25, wherein the
isocyanate comprises one or both of hexamethylenediisocyanate or
1,3-bis(isocyanatemethyl) cyclohexane.
27. A photoelectric conversion device according to claim 25, wherein the
isocyanate has an isocyanate group masked by .epsilon.-caprolactam.
28. A photoelectric conversion device according to claim 21, wherein the
resin comprises an acrylic resin.
29. A photoelectric conversion device according to claim 21, wherein the
resin comprises a resin obtained by crosslinking an acrylic resin and an
inorganic polymer.
30. A photoelectric conversion device according to claim 21, wherein the
photoelectric conversion element is a solar cell element.
31. A solar cell module comprising:
(a) a photoelectric conversion element having a light receiving surface,
(b) a transparent layer provided on said light receiving surface, and
(c) an organic resin layer provided on said transparent layer,
wherein said transparent layer is derived from a resin containing a silane
coupling agent.
32. A solar cell module according to claim 31, wherein the silane coupling
agent includes a compound represented by the general formula XSiY.sub.3,
with X being a reactive organic functional group and Y being a
hydrolyzable group.
33. A solar cell module according to claim 31, wherein the silane coupling
agent includes an epoxy series silane coupling agent.
34. A solar cell module according to claim 33, wherein the epoxy series
silane coupling agent comprises at least one member selected from the
group consisting of
.gamma.-gylcidoxypropyltrimethoxysilane,
.gamma.-gylcidoxypropyltriethoxysilane, and
.beta.-(3,4-epoxycyclohexyl) ethyltrimethoxysilane.
35. A solar cell module according to claim 31, wherein the resin is
crosslinked by an isocyanate.
36. A solar sell module according to claim 35, wherein the isocyanate
comprises one or both of hexamethylenediisocyanate or
1,3-bis(isocyanatemethyl) cyclohexane.
37. A solar cell module according to claim 35, wherein the isocyanate has
an isocyanate group masked by .epsilon.-caprolactam.
38. A solar cell module according to claim 31, wherein the resin comprises
an acrylic resin.
39. A solar cell module according to claim 31, wherein the resin comprises
a resin obtained by crosslinking an acrylic resin and an inorganic
polymer.
40. A solar cell module according to claim 31, wherein the organic resin
layer comprises a transparent thermoplastic polyolefin resin.
41. A solar cell module according to claim 40, wherein the transparent
thermoplastic polyolefin resin is a resin selected from the group
consisting of ethylene-vinyl acetate copolymer and ethylene-ethyl acrylate
copolymer.
42. A solar cell module according to claim 31, wherein the organic resin
layer is a layer formed by means of a film-coating process.
43. A solar cell module according to claim 31, wherein the photoelectric
conversion element comprises an electrically conductive substrate as a
first electrode, a semiconductor active layer which is provided on said
electrically conductive substrate, a transparent and conductive layer as a
second electrode which is provided on said semiconductor layer.
44. A solar cell module according to claim 43, wherein the semiconductor
active layer comprises a non-single crystal semiconductor thin film.
45. A solar cell module according to claim 44, wherein the non-single
crystal semiconductor thin film is composed of an amorphous silicon
material.
46. A solar cell module according to claim 43, wherein the transparent and
conductive layer comprises an ITO film.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved, reliable protective material
for a semiconductor element, a semiconductor element provided with said
protective material, and a semiconductor device provided with said
semiconductor element. More particularly, the present invention relates to
an improved, reliable protective material which can be disposed at the
surface of a semiconductor element including a photoelectric conversion
element such as a solar cell element, specifically, which is suitable for
use as a surface covering material disposed on the light incident side of
said photoelectric conversion element. The present invention also relates
to a semiconductor element including a photoelectric conversion element
such as a solar cell element which is provided with said protective
material, and a semiconductor device provided with said semiconductor
element.
2. Related Background Art
In recent years, societal concern for the problems relating to the
environment and energy sources has been increasing all over the world.
Particularly, heating of the earth because of the so-called greenhouse
effect due to an increase of atmospheric CO.sub.2 has been predicted to
cause a serious problem. In view of this, there is an increased demand for
a means of power generation capable of providing clean energy without
causing CO.sub.2 buildup.
Public attention has been focused on solar cells in order to meet such
demand, because they can supply electric power without causing such a
problem as above mentioned and are expected to be a future power
generation source, and they are safe and easy to handle.
Such solar cells include single crystal silicon solar cells, polycrystal
silicon solar cells, amorphous silicon solar cells (including microcrystal
silicon solar cells), copper indium selenide solar cells, and compound
semiconductor solar cells. Of these solar cells, various studies have been
made on so-called thin film crystal silicon solar cells, compound
semiconductor solar cells, and amorphous silicon solar cells since their
semiconductor active layer can be relatively easily formed in a large area
and in a desired form and they therefore can be easily produced at a
relatively low production cost.
Particularly, thin film amorphous solar cells, specifically, amorphous
silicon solar cells, comprising an electrically conductive metal
substrate, an amorphous silicon semiconductor active layer disposed on
said metal substrate, and a transparent and conductive layer disposed on
said semiconductor active layer have been evaluated as being the most
advantageous among the conventional solar cells because their
semiconductor active layer comprised of amorphous silicon (hereinafter
referred to as a-Si) can be easily formed in a large area and in a desired
form on a relatively inexpensive substrate with a low production cost and
they are light and excel in shock resistance and flexibility, and in
addition, they can be designed into a solar cell module in a desired
configuration which can be used as a power generation source.
Now, in the case of an amorphous silicon solar cell having a semiconductor
active layer comprising, for example, an a-Si thin film disposed on a
glass plate as a substrate, light is impinged through the substrate side,
and because of this, the glass plate can be designed to serve as a
protective member. However, in the case of the aforementioned solar cell
having the a-Si semiconductor active layer disposed on the metal
substrate, because the metal substrate does not permit incident light to
transmit therethrough, light is impinged through the side opposite the
metal substrate, and therefore, it is necessary to dispose an appropriate
transparent protective member on the side through which light is impinged
such that it protects the solar cell element.
SUMMARY OF THE INVENTION
In the conventional semiconductor devices (including the conventional solar
cell modules) having a photoelectric conversion element such as a solar
cell element, the light incident side of the photoelectric conversion
element is protected by a surface covering material comprising a
transparent fluorine-containing polymer film comprised of a fluororesin or
a fluororesin-containing composition as a surface protective member which
is positioned at the outermost surface and a transparent thermoplastic
resin as a filler which is positioned under the transparent
fluorine-containing polymer film.
The fluorine-containing polymer film is often used in the above described
manner, since it is advantageous in that it is satisfactory in terms of
weatherability and water-repellency and serves to reduce deterioration in
the photoelectric conversion efficiency of the photoelectric conversion
element caused due to a reduction in the transmittance of the surface
protective member which occurs when the protective member is yellowed or
clouded as a result of the protective member having been deteriorated. As
for the thermoplastic resin used as the filler in combination with the
fluorine-containing polymer film, it is also often used since it is
relatively inexpensive and suitable for protecting the photoelectric
conversion element and it therefore can be used in a relatively large
amount.
Now, description will be made of such a semiconductor device (a solar cell
module).
FIG. 1 is a schematic cross-sectional view of an example of the solar cell
module. In FIG. 1, reference numeral 101 indicates a transparent
fluorine-containing polymer thin film layer as an outermost surface
protective layer, reference numeral 102 a transparent thermoplastic resin
layer which is situated under the fluorine-containing thin film layer 101,
reference numeral 106 a solar cell element comprising a photovoltaic
element 104 and a transparent resin thin film layer 103 disposed on the
surface of said photovoltaic element, and reference numeral 105 an
insulating layer. In this solar cell module, the solar cell element 106 is
enclosed by the transparent thermoplastic resin layer 102 which serves as
a filler.
Specifically, the fluorine-containing polymer thin film layer 101 comprises
a fluororesin film selected from the group consisting of ETFE
(ethylene-tetrafluoro-ethylene copolymer) film, PVF (polyvinyl fluoride)
film, and the like. The transparent thermoplastic resin layer 105
comprises a thermoplastic resin selected from the group consisting of EVA
(ethylene-vinyl acetate copolymer), EEA (ethylene-acrylic ester
copolymer), and butyral resin. The transparent resin thin film layer 103
comprises a resin film composed of an acrylic resin, a fluororesin, or an
acrylic resin crosslinked with an inorganic polymer. The insulating layer
105 comprises an organic resin film such as nylon film, TEDLAR (trademark
name, laminated aluminum foil), or the like.
In the above described solar cell module, the transparent thermoplastic
resin layer 102 serves not only as an adhesive between the photovoltaic
element 104 and the fluororesin film 101 as the surface protective layer
but also as an adhesive between the photovoltaic element and the
insulating layer 105. The transparent resin thin film layer 103 disposed
on the photovoltaic element 104 serves to electrically isolate the
photovoltaic element from the outside of the module. In addition, the
transparent resin thin film layer 103 in combination with the transparent
thermoplastic resin layer 102 serves as a filler for preventing the
photovoltaic element 104 from being damaged and subjected to external
shocks. The insulating layer 105 serves to reinforce the solar cell module
while adding an appropriate rigidity thereto.
As for the solar cell module thus constituted, it is often configured so
that it can be placed on the roof of a building or integrated with the
roof of a building. In this case, it is necessary to meet the roofing
standards prescribed in each country. The roofing standards sometimes
include a combustion test. In order to clear the combustion test, it is
desired that the amount of EVA as a combustible resin used as the filler
in the solar cell module be reduced as much as possible. However, when the
amount of the EVA used in the solar cell module is simply reduced, a
problem ensues in that the performance of the surface covering material
which protects the photovoltaic element is reduced as the amount of the
EVA used is reduced.
In order to solve this problem, there is known a process wherein a
transparent resin thin film layer composed of a fire-retarding or
incombustible transparent resin is disposed in the surface covering
material and the thickness of the EVA layer is thinned as desired, thereby
attaining incombustibility of the solar cell module without reducing the
performance of the surface covering material protecting the photovoltaic
element. According to this process, for instance, it is possible to attain
a solar cell which can be classified into Class A in the combustion test
in the standard UL 1703 of the U.S.A. that prescribes a solar cell module
which can be used as a roofing material.
Now, as for the above described fire-retarding or incombustible transparent
resin thin film layer, it is usually formed of a resin obtained by
crosslinking an acrylic resin or a fluororesin with isocyanate as a
crosslinking agent. The coating composition containing isocyanate used for
the formation of the fire-retarding or incombustible transparent resin
thin film layer in this case includes a one liquid type coating
composition in which isocyanate is previously mixed with a resin (an
acrylic resin or a fluororesin) and a two-liquid type coating composition
in which the two materials (that is, the isocyanate and resin) are mixed
immediately before the formation of a film.
The two-liquid type coating composition is problematic in that the
apparatus used for the formation of a film using the two-liquid type
coating composition is unavoidably complicated because the two materials
are mixed immediately before the film formation and in addition, the pot
life of the resin after the admixture is liable to be short. For this
reason, the one liquid type coating composition is usually used,
specifically, a one-liquid type coating composition using a so-called
blocking isocyanate which is used in a manner of masking a highly reactive
isocyanate group by a blocking agent and dissociating the blocking agent
by virtue of heat energy to regenerate the isocyanate group so as to
dedicate it for the crosslinking reaction for the resin. The blocking
agent used for masking the isocyanate group in this case includes MEK
(methyl ethyl ketone) oxime and .epsilon.-caprolactam. In the case where
MEK oxime is used, a problem is liable to ensue in that yellowing occurs
when the resulting coating film is subjected to heat treatment. Therefore,
in the case where a transparent film is intended to be formed,
.epsilon.-caprolactam is intentionally used.
Now, in the case of a solar cell module having a surface covering material
constituted by a laminate comprising such a fire-retarding or
incombustible transparent resin thin film layer as above described and a
transparent thermoplastic resin layer composed of EVA for example, such
problems as will be described in the following are liable to occur.
That is, when the solar cell module is continuously exposed to sunlight in
the outdoors over a long period of time, the temperature of the surface of
the photovoltaic element may increase to 65.degree. C. or more, whereby
the surface covering material is yellowed. This problem is liable to
become significant in the case where the solar cell module is used while
being integrated with the roof of a building, whereby the temperature of
the solar cell module is further increased. This situation occurs because
the blocking agent dissociated upon the crosslinking of the resin remains
in the coating film without being volatilized and reacts with a peroxide
used for the crosslinking of the EVA and/or an acid generated upon the
crosslinking of the EVA, thereby causing the formation of a yellowed
product with reduced light transmissivity of the surface covering
material, resulting in deteriorating the characteristics of the solar cell
module.
In addition, when the solar cell module is continuously used in a severe
outdoor atmosphere of high temperature and high humidity over a long
period of time, a removal of the constituents of the surface covering
material and also at the interface between the surface covering material
and the photovoltaic element is liable to occur, resulting in not only
deteriorating the characteristics of the solar cell module but also
deteriorating the exterior appearance of the solar cell module.
In order to prevent the surface covering material from being yellowed due
to heat degradation or light fatigue of the resin, the use of a primary
antioxidant comprising a hindered phenol series antioxidant and a
secondary antioxidant comprising a phosphorous series antioxidant in
combination is known. However, the above described problems cannot be
sufficiently solved by using the aforesaid two antioxidants in
combination.
In view of this, there is a demand for providing an improved solar cell
module which is free of the above problems.
The present invention is aimed at eliminating the foregoing problems found
in the conventional surface covering material for a semiconductor element
and providing an improved, highly reliable surface covering material for
said semiconductor element which is free of the problems in the prior art,
wherein said surface covering material excels in adhesion with the
semiconductor element, is hardly yellowed and exhibits a desirable
transmissivity without being deteriorated and without causing a separation
between it and the semiconductor element even upon continuous exposure to
a severe atmosphere with a high temperature and high humidity over a long
period of time, and it enables manufacture of a highly reliable module of
the semiconductor element which stably exhibits desirable module
characteristics without being deteriorated even when it in continuously
used under severe environmental conditions with a high humidity and with
frequent changes in the environmental temperature over a long period of
time.
The term "semiconductor element" in the present invention is meant to
include a photoelectric conversion element, including a solar cell
element.
Another object of the present invention is to provide an improved, highly
reliable surface covering material comprising a specific transparent resin
layer for a semiconductor element, said transparent resin layer being
formed of a resin containing at least a silane coupling agent.
A further object of the present invention is to provide a highly reliable
semiconductor element provided with an improved, highly reliable surface
covering material comprising a specific transparent resin layer, said
transparent resin layer being formed of a resin containing at least a
silane coupling agent.
A further object of the present invention is to provide a highly reliable
semiconductor device provided with an improved, highly reliable surface
covering material comprising a specific transparent resin layer and at
least a transparent organic resin layer disposed on said specific
transparent resin layer, said specific transparent resin layer being
formed of a resin containing at least a silane coupling agent.
According to the present invention, there are provided such advantages as
will be described in the following.
(1) There can be attained a highly reliable incombustible surface coating
for a solar cell module. Particularly, by reducing the amount of the
combustible resin used in the surface covering resin material in the prior
art, there can be attained a highly incombustible solar cell module.
(2) There can be attained a highly reliable surface coating for a solar
cell module excelling in heat resistance. Particularly, there can be
attained a highly reliable surface covering material comprising a coating
film in which the amount of the residual blocking agent is slight and
which is free of the problem found in the prior art in that the
conventional surface covering material is yellowed upon continuous use
under environmental conditions with a high temperature.
(3) There can be attained a highly reliable surface coating excelling in
moisture resistance for a solar cell module which effectively prevents
moisture invasion, wherein the solar cell module does not suffer from a
reduction in its characteristics due to invaded moisture.
(4) There can be attained a highly reliable surface coat excelling in
adhesion for a solar cell module. Particularly, there can be attained a
highly reliable surface covering material which is free of the problem
found in the prior art in that the conventional surface covering material
is liable to separate from the solar cell element (or the photoelectric
conversion element) upon continuous use under environmental conditions
with a high temperature and high humidity, wherein the solar cell module
does not suffer from a reduction in its characteristics due to such
separation.
(5) There can be attained a highly reliable surface coating having an
excellent electrically insulating property for a solar cell module.
Particularly, there can be attained a highly reliable surface covering
material which effectively prevents electric current generated by a solar
cell element (or a photoelectric conversion element) from leaking to the
outside and always maintains the solar cell element in a state of being
electrically isolated from the exterior.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic cross-sectional view illustrating the constitution of
a conventional solar cell module as a semiconductor device.
FIG. 2 is a schematic cross-sectional view illustrating the constitution of
an example of a solar cell module as a semiconductor device according to
the present invention.
FIG. 3 is a schematic cross-sectional view illustrating the constitution of
an example of a photoelectric conversion element which can be used in the
present invention.
FIG. 4 is a schematic cross-sectional view illustrating the constitution of
another example of a solar cell module as a semiconductor device according
to the present invention.
FIG. 5 is a schematic view for explaining the scratch resistance test which
will be later described.
DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
The present invention intends to eliminate the foregoing problems in the
prior art and to attain the above described objects.
The present invention will now be described in detail while referring to
the drawings.
FIG. 2 is a schematic cross-sectional view illustrating an example of a
solar cell module as a semiconductor device according to the present
invention.
In FIG. 2, reference numeral 201 indicates a photovoltaic element (or a
photoelectric conversion element), reference numeral 202 a transparent
resin layer (comprising a transparent resin thin film) reference numeral
203 a transparent front surface side filler (comprising a transparent
organic high-molecular weight resin layer), reference numeral 204 a
transparent film which is positioned at the outermost surface (this film
will be hereinafter referred to as front surface protective film or front
surface protective layer), reference numeral 205 a filler on the rear side
of the photovoltaic element 201 (this filler will be hereinafter referred
to as backside filler), and reference numeral 206 a back face protective
film. Reference numeral 207 indicates a solar cell element comprising the
photovoltaic element 201 and the transparent resin layer 202.
In the solar cell module shown in FIG. 2, light is impinged through the
outermost surface film 204, and the light impinged passes through the
transparent outermost surface film 204, transparent filler 203 and
transparent resin layer 202 to arrive in the photovoltaic element 201.
Photoelectromotive force generated in the photovoltaic element 201 is
outputted through output terminals (not shown).
The photovoltaic element 201 comprises at least a semiconductor active
layer as a photoelectric conversion member disposed on an electrically
conductive substrate.
FIG. 3 is a schematic cross-sectional view illustrating the constitution of
such photovoltaic element.
In FIG. 3, reference numeral 301 indicates an electrically conductive
substrate, reference numeral 302 a back reflecting layer, reference
numeral 303 a semiconductor active layer, reference numeral 304 a
transparent and conductive layer, reference numeral 305 a collecting
electrode (or a grid electrode), reference numeral 306a a power output
terminal on the positive side, reference numeral 306b a power output
terminal on the negative side, and reference numeral 307 an electrically
connecting means.
As apparent from FIG. 3, the photovoltaic element comprises the back
reflecting layer 302, the semiconductor active layer 303, the transparent
and conductive layer 304, and the collecting electrode 305 disposed in
this order on the electrically conductive substrate 301, wherein the
output terminal 306a is electrically connected to the collecting electrode
305 by means of the electrically conductive paste or solder 307 and it
extends from the collecting electrode while being insulated by means of an
insulating member (not shown), and the output terminal 306b is
electrically connected to the electrically conductive substrate 301 by
means of solder (not shown). In this configuration, the positive side
power output terminal and the negative side power output terminal may be
changed into a negative side power output terminal and a positive side
power output terminal depending upon the constitution of the semiconductor
active layer.
The electrically conductive substrate 301 serves not only as a substrate
for the photovoltaic element but also as a lower electrode. As for the
electrically conductive substrate 301, there is no particular restriction
as long as it has an electrically conductive surface. Specifically, it may
be an electrically conductive member composed of a metal such as Ta, Mo,
W, A1, Cu, Ti, or the like, or an electrically conductive member composed
of an alloy such as stainless steel, or the like. Besides these, the
electrically conductive substrate may comprise a carbon sheet or a
Pb-plated steel sheet. Alternatively, the electrically conductive
substrate may be a film or sheet made of a synthetic resin or a sheet made
of a ceramic. In this case, the substrate is coated with an electrically
conductive film on the surface thereof.
The back reflecting layer 302 disposed on the electroconductive substrate
301 may comprise a metal layer, a metal oxide layer, or a two-layered
structure comprising a metal layer and a metal oxide layer. The metal
layer may comprise a metal such as Ti, Cr, Mo, W, A1, Ag, or Ni, or an
alloy of these metals. The metal oxide layer may comprise a conductive
metal oxide such as ZnO, SnO.sub.2, or the like.
The metal layer and metal oxide layer as the back reflecting layer 302 may
be formed by means of a conventional film-forming process such as
resistance heating evaporation, electron beam evaporation, or sputtering.
The back reflecting layer 302 is desired to have a roughened surface in
order to effectively utilize incident light.
The semiconductor active layer 303 functions to conduct photoelectric
conversion. The semiconductor active layer 303 may be composed of a
non-single crystal silicon semiconductor material such as an amorphous
silicon semiconductor material or polycrystalline silicon semiconductor
material, or a compound semiconductor material. In any case, the
semiconductor active layer comprised of any of these semiconductor
materials may be of a stacked structure with a pn junction, a pin
junction, or a Schottky type junction.
Specific examples of compound semiconductor materials are CuInSe.sub.2,
CuInS.sub.2, GaAs, CdS/CU.sub.2 S/CdTe, CdS/InP, CdTe/Cu.sub.2 Te, and the
like.
The semiconductor active layer comprised of any of the above mentioned
semiconductor materials may be formed by a conventional film-forming
process. For instance, the non-single crystal silicon semiconductor active
layer may be formed by a conventional chemical vapor phase growing process
such as plasma CVD or photo-induced CVD using a suitable film-forming raw
material gas capable of supplying silicon atoms, such as silane gas or a
conventional physical vapor phase growing process such as sputtering or
the like. The semiconductor active layer composed of a polycrystalline
silicon semiconductor material may be formed by a conventional
polycrystalline silicon film-forming process of providing a fused silicon
material and subjecting the fused silicon material to film-deposition
processing or another conventional polycrystalline silicon film-forming
process of subjecting an amorphous silicon material to heat treatment.
The semiconductor active layer composed of any of the above mentioned
compound semiconductor materials may be formed by means of ion plating,
ion beam deposition, vacuum evaporation, sputtering, or an electrolytic
technique in which a deposit is formed by electrolysis of a desired
electrolyte.
The transparent and conductive layer 304 functions as an upper electrode.
The transparent and conductive layer may comprise In.sub.2 O.sub.3,
SnO.sub.2, In.sub.2 O.sub.3 -SnO.sub.2 (ITO), ZnO, TiO.sub.2, or Cd.sub.2
SnO.sub.4. Alternatively, it may comprise a crystalline semiconductor
layer doped with an appropriate impurity at a high concentration.
The transparent and conductive layer constituted by any of the above
mentioned materials may be formed by means of resistance heating
evaporation, electron beam evaporation, sputtering, spraying, or CVD.
The above described impurity-doped crystalline semiconductor layer as the
transparent and conductive layer may be formed by a conventional
impurity-diffusion film-forming method.
Now, for a stacked body (as a photovoltaic element) 303, there may occur a
condition that the electrically conductive substrate 301 and the
transparent and conductive layer 304 are partially short-circuited due to
an unevenness in the surface of the electrically conductive substrate
and/or an unevenness in the semiconductor active layer 303 which occurs
upon the formation thereof, whereby a relatively large leakage current
flows in proportion to the voltage outputted, namely, there is a low leak
resistance (or shunt resistance). The stacked body (the photovoltaic
element) having such defects is desired to be repaired in a defect-free
state by eliminating the defect. This can be conducted, for example, in
accordance with the defect-repairing manner described in U.S. Pat. No.
4,729,970. In this case, the defect-bearing stacked body is desired to be
repaired to have a shunt resistance preferably in the range of from 1
k.OMEGA..cm.sup.2 to 500 k.OMEGA..cm.sup.2 or more preferably in the range
of from 10 k.OMEGA.cm.sup.2 to 500 k.OMEGA..cm.sup.2.
For the purpose of efficiently collecting an electric current generated by
the photoelectromotive force, the collecting electrode (or the grid
electrode) 305 may be disposed on the transparent and conductive layer
304. The collecting electrode 305 may be in the form of a stripe shape or
comb shape.
The collecting electrode 305 may comprise a metal such as Ti, Cr, Mo, W,
A1, Ag, Ni, Cu, or Sn, or an alloy of these metals. Alternatively, the
collecting electrode may be formed of an electrically conductive paste or
an electrically conductive resin. The electrically conductive paste can
include electrically conductive pastes comprising powdered Ag, Au, Cu, Ni,
or carbon dispersed in an appropriate binder resin. The binder resin
herein can include polyester, epoxy resin, acrylic resin, alkyd resin,
polyvinyl acetate, rubber, urethane resin, and phenol resin.
The collecting electrode 305 may be formed by means of sputtering using a
patterned mask, resistance heating evaporation, or CVD. It may also be
formed by depositing a metal film over the entire surface and subjecting
the metal film to an etching treatment to form a desired pattern, by
directly forming a grid electrode pattern by means of photo-induced CVD,
or by forming a negative pattern corresponding to a grid electrode pattern
and subjecting the resultant to plating treatment.
The formation of the collecting electrode using any of the above described
electrically conductive pastes can be conducted by subjecting the
electrically conductive paste to screen printing or fixing a metal wire to
the screen-printed electrically conductive paste, if necessary, using a
solder.
The output terminals 306a and 306b serve to output electromotive force. The
output terminal 306a is electrically connected to the collecting electrode
305 by means of the electrically connecting means 307 comprising an
electrically conductive paste or a solder. The output terminal 306b is
electrically connected to the electrically conductive substrate 301 by
spot welding or soldering an appropriate metal body such as copper tab.
In general, there are provided a plurality of photovoltaic elements having
the above constitution, and they are integrated in series connection or in
parallel connection depending upon the desired voltage or current. It is
possible to dispose the integrated body on an insulating member such that
a desired voltage or electric current can be obtained.
Description will now be made of the surface protective film 204 (or the
surface protective layer).
The surface protective film 204 is positioned at the outermost surface of
the solar cell module and because of this, it is required to excel in
transparency, weatherability, water repellency, heat resistance, pollution
resistance, and physical strength. In addition, in the case where the
solar cell module is used outdoors, it is required that the surface
protective film ensure that the solar cell module is of sufficient
durability upon repeated use over a long period of time.
In order for the surface protective film to satisfy all these conditions,
the surface protective film comprises a film composed of a highly
transparent fluororesin. Specific examples of such highly transparent
fluororesin are tetrafluoroethylene-ethylene copolymer (ETFE), polyvinyl
fluoride resin (PVF), polyvinylidene fluoride resin (PVDF),
polytetrafluoroethylene resin (TFE),
tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and
polychlorotrifluoroethylene resin (CTFE). Of these fluororesins, PVF is
most excellent in view of weatherability. And in view of weatherability
and physical strength in combination, ETFE is most excellent.
In order to attain an improvement in the adhesion of the surface protective
film 204 with the surface side filler 203, a given surface of the surface
protective film to be contacted with the surface side filler is subjected
to surface treatment upon its lamination to the surface side filler. The
surface treatment in this case can include corona discharging treatment
and plasma treatment. In order for the surface protective film to have an
improved physical strength, it is desired that the surface protective film
comprises ah oriented film. Further, in order to attain an improvement in
the weatherability of the surface protective layer, it is possible to make
the surface protective film such that it has an outermost surface coated
with SiO.sub.X.
Description will now be made of the front surface side filler 203 (the
transparent organic high-molecular resin layer).
The front surface side filler 203 serves to cover the photovoltaic element
with a resin so as to protect it from the external environment. In
addition, the front surface side filler serves to bond the front surface
protective film with the photovoltaic element. Hence, the front surface
side filler is required to be highly transparent, and to excel in
weatherability, adhesion, and heat resistance. In order for the front
surface side filler to meet these conditions, the front surface side
filler is desired to comprise a thermoplastic resin selected from the
group consisting of polyolefinic resins, butyral resins, silicone resins,
epoxy resins, and acrylic resins.
Preferable specific examples of such thermoplastic resin are ethylene-vinyl
acetate copolymer (EVA), ethylene-methyl acrylate copolymer (EMA),
ethylene-ethyl acrylate copolymer (EEA), ethylene-butyl acrylate copolymer
(EBA), ethylene-methyl methacrylate copolymer (EMM), ethylene-ethyl
methacrylate copolymer (EEM), and polyvinyl butyral (PVB). Of these
resins, EVA and EEA are the most appropriate in view of availability and
from an economical viewpoint.
Any of the above mentioned resins usable as the front surface side filler
(this resin will be hereinafter referred to as filler resin) has a low
heat deformation temperature and is liable to readily deform or creep at a
high temperature. Because of this, the filler resin is desired to be
crosslinked with an appropriate crosslinking agent so that it has an
increased heat resistance and adhesion property. The crosslinking agent
usable in this case can include isocyanates, melamines, and organic
peroxides. In any case, the crosslinking agent is desired to be one which
has a sufficiently long pot life and quickly causes crosslinking of the
filler resin. Further, since the front surface protective film is
laminated on the front surface side filler, it is desired for the
crosslinking agent to be one that causes no or only a slight amount of
free material from the crosslinking agent to remain.
In addition, the front surface side filler may contain an antioxidant in
order to prevent it from being thermally oxidized. Further in addition, in
order to prevent the front surface side filler from being deteriorated by
light impingement, the front surface side filler may contain an UV
absorber and/or a light stabilizer.
In the case where the adhesion of the front surface side filler with the
photovoltaic element or the surface protective film is not sufficient, the
adhesion can be improved by incorporating into the front surface side
filler a silane coupling agent and a titanate coupling agent either singly
or in combination.
Description will now be made of the transparent resin thin film layer 202
(or the transparent resin layer).
The transparent resin thin film layer 202 serves to coat the irregularities
of the photovoltaic element while protecting the photovoltaic element from
the external environment in combination with the front surface side
filler. The transparent resin thin film layer 202 also serves to maintain
the photovoltaic element electrically isolated from the exterior. As well
as in the case of the front surface side filler 203, the transparent resin
thin film 202 is required to be highly transparent, and to excel in
weatherability, adhesion, and heat resistance.
In order for the transparent resin thin film layer 202 to meet these
conditions, the transparent resin thin film layer is mainly comprised of a
transparent resin selected from the group consisting of resins comprising
acrylic resins, silicone resins, or fluororesins. Preferable specific
examples of such resin are resins obtained by crosslinking an acrylic
resin and an inorganic polymer with an appropriate crosslinking agent,
silicone series resins such as alkoxysilazanes, and fluororesins.
The above acrylic resin can include resins obtained by polymerizing a
methacrylic monomer selected from the group consisting of methyl
methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate,
methacrylic acid, diethylaminoethyl methacrylate, 2-hydroxyethyl
methacrylate, tert-butylaminoethyl methacrylate, 2-hydroxypropyl
methacrylate, dimethylaminoethyl methacrylate, ethylene dimethacrylate,
ethylene glycol dimethacrylate, and 1,3-butylene dimethacrylate, and a
monomer selected from the group consisting of isobutyl acrylate, acrylic
acid diethyleneglycolethoxylate, 2-hydroxyethyl acrylate, and
2-hydroxypropylacrylate.
The above inorganic polymer can include polymers of silicon compounds such
as siloxane, silazane, metallosiloxane, metallosilazane, and mixtures of
these polymers.
As the crosslinking agent used for crosslinking the acrylic resin and
inorganic polymer, it is desired to use a crosslinking agent which has a
sufficiently long pot life and which quickly causes crosslinking reaction
between the acrylic polymer and inorganic polymer to produce a crosslinked
resin in a state containing no free material from the crosslinking agent
or only a slight amount of said free material if it should be contained
therein.
There can be mentioned blocking isocyanates as crosslinking agents which
meet these conditions.
In terms of chemical structure of the isocyanate monomer for such blocking
isocyanate, there can be mentioned tolylenediisocyanate,
isophoronediisocyanate (IPDI), xylenediisocyanate (XDI),
1,3-bis(isocyanatomethyl)cyclohexane (H.sub.6 XDI),
hexamethylenediisocyanate (HDI), tetramethylxylylenediisocyanate, and
m-isopropenyl-.alpha.,.alpha.-dimethylbenzylisocyanate.
In the case where an excellent transparency is required, XDI which is of
yellowing retardant type, and IPDI, H.sub.6 XDI, and HDI which are of
non-yellowing type are desired to be used.
The above mentioned isocyanate monomers are generally used as an isocyanate
prepolymer. And they are roughly divided into adduct series of
tetramethylene propanol (TMP) (or TMP adducts in other words), biuret
series, isocyanurate series and alphanate series. In order for the
transparent resin thin film layer to have an improved weatherability and
heat resistance, a TMP adduct or isocyanurate is desired to be used.
As the blocking agent for the isocyanate, there can be mentioned oximes
such as ethylacetoacetate and methyl ethyl ketone (MEK) oxime, lactams
such as .epsilon.-caprolactam, phenols, and alcohols. In order to prevent
a resin thin film as the transparent resin thin film layer from being
yellowed upon the formation thereof or upon use under high temperature
conditions, it is desired to use .epsilon.-caprolactam or alcohols.
In order to make a resin thin film used as the transparent resin thin film
layer to be desirably heat resistant when used under conditions of high
temperature, the resin thin film may contain an antioxidant in an amount
of 0.05 to 1.0 wt. % versus the total amount of the resin components of
the resin film.
Such antioxidant can include monophenol series antioxidants, bisphenol
series antioxidants, high-molecular phenol series antioxidants, sulphur
series antioxidants, and phosphorous series antioxidant
Specific examples of the monophenol series antioxidants are
2,6-di-tert-butyl-p-cresol, butylated hydroxyanisol, and
2,6-di-tert-butyl-4-ethylphenol.
Specific examples of the bisphenol series antioxidants are
2,2'-methylene-bis-(4-methyl-6-tert-butylphenol),
2,2'-methylene-bis-(4-ethyl-6-tert-butylphenol),
4,4'-thiobis-(3-methyl-6-tert-butylphenol),
4,4'-butylidene-bis-(3-methyl-6-tert-butylphenol), and
3,9-[1,1-dimethyl-2-{.beta.-(3-tert-butyl-4-hydroxy-5-methyl
phenyl)propyonyloxy ethyl}2,4,8,10-tetraoxapyro] 5,5 undecane.
Specific examples of the high-molecular phenol series antioxidants are
1,1,3-tris-(2-methyl-4-hydroxy-5-tert-butylphenyl)butane,
1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl)benzene,
tetrakis-methylene-3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate
methane, bis 3,3'-bis-(4'-hydroxy-3'tert-butylphenyl)butyric acid
glucoseester,
1,3,5-tris(3',5'-di-tert-butyl-4'-hydoxylbenzyl)-s-triazine-2,4,6-(1H,3H,5
H)trion, and tocopherol (Vitamin E).
Specific examples of the sulphur series antioxidants are
dilaurylthiodipropionate, dimyristylthlodipropionate, and
distearylthiopropionate.
Specific examples of the phosphorous series antioxidants are
triphenylphosphate, diphenylisodecylphosphate, phenyldiisodecylphosphate,
4,4'-butylidene-bis-(3-methyl-6-tert-butylphenyl-di-tridecyl)phosphate,
cyclicneopentanetetrabis (octadecylphosphate), tris(mono or
di)phenylphosphate, diisodecylpentaerythritoldiphosphate,
9,10-dihydro-9-oxa-10-phosphenanthrene-10-oxide, 10-(3,5-di-tert-butyl-4
-hydroxybenzyl)-9,10-dihydro-9-oxa-10phosphenanthrene-10-oxide,
10-decyloxy-9,10-dihydro-9-oxa-10-phosphenanthrene,
cyclicneopentanetetrabis(2,4-di-tert-butylphenyl)phosphate,
cyclicneopentanetetrabis (2,6-di-tert-methylphenyl)phosphate, and
2,2-methylenebis(4,6-tert-butylphenyl)octylphosphate.
These antioxidants may be used either singly or in a combination of two or
more of them.
Further, in order for the resin thin film as the transparent resin thin
film layer to have an improved adhesion, the resin film may contain a
silane coupling agent in an amount of 0.1 to 10 wt. % versus the total
amount of the resin components of the resin film.
Such silane coupling agent in terms of chemical structure can include
compounds represented by the general formula XSiY.sub.3, with X being a
reactive organic functional group and Y being a hydrolyzable group. The
reactive organic functional group X can include an amino group,
.gamma.-glycidoxypropyl group, vinyl group, methacryl group, mercapto
group, and chlorine group. The hydrolyzable group Y can include alkoxy
groups such as a methoxy group and an ethoxy group. Of these groups, the
.gamma.-glycidoxypropyl group is the most appropriate as the group X, and
the methoxy group is the most appropriate as the group Y.
Specific examples of these compounds are
.gamma.-(2-aminoethyl)aminopropyltrimethoxysilane,
.gamma.-(2-aminoethyl)aminopropyldimethoxysilane,
.gamma.-methacryloxypropyltrimethoxysilane,
.gamma.-(2-aminoethyl)aminopropyltrimethoxysilane,
.gamma.-glycidoxypropyltrimethoxysilane,
.gamma.-mercaptopropyltrimethoxysilane, vinyltrimethoxysilane,
hexamethyldisilazane,
.gamma.-allynynopropyltrimethoxysilane, and
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.
Specifically, epoxy series silane coupling agents such as
.gamma.-glycidoxypropyltrimethoxysilane,
.gamma.-glycidoxypropyltriethoxysilane, and
.beta.-(3,4-epoxycyclohexyl)ethyltrimethoxysilane are desirably used. Of
these, .gamma.-glycidoxypropyltrimethoxysilane is the most desirable since
if it used as the silane coupling agent, an improvement can be attained
not only in the adhesion but also in the heat resistance of the resin thin
film as the transparent resin thin film layer.
Further, the resin thin film as the transparent resin thin film layer may
contain fine particles of an appropriate inorganic oxide (this will be
hereinafter referred to as inorganic oxide fine particles).
Specific examples of such inorganic oxide are silicon oxide, zinc oxide,
tin oxide, titanium oxide, and aluminum oxide.
The added inorganic oxide fine particles are of a mean particle size
preferably in the range of from 1 .mu.m to 1000 .mu.m or more preferably
in the range of from 5 .mu.m to 100 .mu.m.
As for the amount of the inorganic oxide fine particles to be added, when
it is excessive, a problem is liable to entail in that light does not
sufficiently arrive at the photovoltaic element. It is preferably in the
range of from 0.1 wt. % to 20 wt. % or more preferably in the range of
from 0.2 wt. % to 10 wt. %.
The incorporation of the inorganic oxide fine particles in a desired amount
within the above range into the transparent resin thin film layer provides
advantages such that incident light is desirably scattered to improve the
photoelectric conversion efficiency, and the hardness of the transparent
resin thin film layer is increased and as a result, the performance of the
transparent resin thin film layer as the protective layer for the
photovoltaic element is improved, wherein particularly, the weatherability
of the transparent resin thin film layer is improved.
The incorporation of the inorganic oxide fine particles into the
transparent resin thin film layer may be conducted by adding fine
particles of any of the foregoing inorganic oxides to a given resin used
for the formation of the transparent resin thin film layer or by forming a
resin thin film as the transparent resin thin film layer and spraying fine
particles of any of the foregoing inorganic oxides onto the resin thin
film.
Description will now be made of the backside filler 205 disposed on the
rear side of the photovoltaic element 201.
The backside filler 205 serves to provide sufficient adhesion between the
photovoltaic element 201 and the back face protective film 206. The
backside filler 205 is desired to comprise a material capable of ensuring
sufficient adhesion between the electrically conductive substrate of the
photovoltaic element and the back face protective film and which excels in
durability, withstands thermal expansion and thermal contraction, and
excels in flexibility. Specific examples of such material are hot-melt
materials such as EVA (ethylene-vinyl acetate copolymer), polyvinyl
butyral, and epoxy adhesives. Besides these, double-coated tapes may be
also usable.
Alternatively, the backside filler 205 may comprise the same resin material
used for the front surface side filler 203.
When the solar cell module is one which is used under environmental
conditions of a high temperature, for instance, when integrated to a roof
of a building in order to use it outdoors, it is desired to use as the
backside filler a material capable of being crosslinked in order to attain
a further improved adhesion between the electrically conductive substrate
of the photovoltaic element and the back face protective film so that the
solar cell module can endure repeated use at high temperature.
Incidentally, resin materials such as EVA can be desirably crosslinked
with the use of an organic peroxide.
Description will now be made of the back face protective film 206.
The back face protective film 206 is disposed for the purpose of
electrically isolating the electrically conductive substrate of the
photovoltaic element 201 from the outside. The back face protective film
206 is desired to be composed of a material which can sufficiently
electrically isolate the electrically conductive substrate of the
photovoltaic element, excels in durability, withstands thermal expansion
and thermal contraction, and excels in flexibility. Specific examples of
such material are laminated films comprising a nylon film or a PET
(polyethylene terephthalate) film, having an adhesive layer composed of a
polyolefin resin on both faces. The polyolefin resin can include
ethylene-vinyl acetate copolymer (EVA), ethylene-methyl acrylate copolymer
(EMA), and ethylene-ethyl acrylate copolymer (EEA).
In the present invention, it is possible to dispose a back face reinforcing
member (not shown in the figure) outside the back face protective film 206
in order to improve the mechanical strength of the solar cell module and
in order to prevent the solar cell module from being distorted or warped
due to changes in the environmental temperature. The back face reinforcing
member may comprise a steel plate, a plastic plate, or a fiber-glass
reinforced plastic plate (a so-called FRP plate).
Now, in order to prevent a decrease in the quantity of incident light
arriving in the photovoltaic element, the surface covering material
comprising the transparent resin thin film layer 202, the transparent
front surface side filler 203 and the front surface protective film 204
which are stacked in the named order from the photovoltaic element side,
is desired to be substantially transparent.
Specifically, it is desired for the surface covering material to have a
transmittance in a visible light wavelength region of 400 nm to 800 nm of
preferably 80% or more preferably 90% or more. Further, in order to
facilitate external light entrance into the photovoltaic element, the
front surface covering material is made such that it has a refractive
index of preferably 1.1 to 2.0, more preferably 1.1 to 1.6 at a
temperature of 25.degree. C.
In the following, description will be made of a manner of producing a solar
cell module as a semiconductor device according to the present invention
using the foregoing photovoltaic element (or photoelectric conversion
element), transparent resin thin film layer, filler resin, front surface
protective film, and back face protective material.
Coating of the light receiving face of the photovoltaic element by the
transparent resin thin film layer may be conducted by applying a coating
liquid comprising a given resin for the formation of the transparent resin
thin film layer dissolved in a solvent. The application of the coating
liquid onto the light receiving face of the photovoltaic element may be
conducted by dipping the photovoltaic element in the coating liquid to
form a coating film covering the light receiving face of the photovoltaic
element; by air-spraying the coating liquid in an atomized state over the
light receiving face of the photovoltaic element to form a coating film
covering the light receiving face of the photovoltaic element; or by
air-spraying the coating liquid in the liquid state over the light
receiving face of the photovoltaic element to form a coating film covering
the light receiving face of the photovoltaic element. In any case, the
coating film formed on the photovoltaic element is subjected to
crosslinking treatment while evaporating the solvent or after the solvent
has been vaporized. Besides these methods, the formation of the
transparent resin thin film layer on the photovoltaic element may be
conducted by providing a given resin in a powdered form for the formation
of the transparent resin thin film layer, depositing the powdered resin on
the light receiving face of the photovoltaic element by electrostatic
adsorption to form a coating film of covering the light receiving face of
the photovoltaic element, and subjecting the coating film to heat
treatment to crosslink it.
Coating of the light receiving face of the photovoltaic element
(particularly, the light receiving face of the solar cell element 207
(see, FIG. 2)) by the front surface side filler may be conducted by (a)
applying a coating liquid comprising a filler resin material dissolved in
a solvent onto the light receiving face and vaporizing the solvent of the
applied coating liquid; (b) by uniformly depositing a powdered filler
resin material on the light receiving face and subjecting the deposited
powdered filler resin material to heat fusion; (c) by providing a
heat-fused product of a filler resin material and applying the heat-fused
product onto the light receiving face through a slit; or (d) by obtaining
a sheet of a filler resin material using a heat-fused product of the
filler resin material and laminating the sheet on the light receiving face
by way of thermocompression bonding.
In the case of the above manner (a), if necessary, one or more of desired
additives such as a silane coupling agent, UV absorber, antioxidant and
the like are firstly mixed with the solvent prior to dissolving the filler
resin material therein, and the resultant coating liquid is applied onto
the light receiving face of the photovoltaic element, followed by drying.
Similarly, in any of the remaining methods (b) to (d), in the case of using
one or more of said desired additives, such additive is added to the
filler resin material prior to heat-fusing the filler resin material.
In the case where the front surface side filler 203 has been previously
formed on the light receiving face of the solar cell element 207 (see,
FIG. 2), the surface protective film 204 is laminated on the front surface
side filler and the back side filler resin material 205 and the back face
protective film 206 are laminated on the rear face of the solar cell
element to obtain a composite, and the resultant composite is subjected to
thermocompression bonding, whereby a desirable solar cell module can be
obtained. In the case where the back face reinforcing member is intended
to be disposed, it is possible for the back face reinforcing member to be
laminated to the back face protective film by means of an appropriate
adhesive. The lamination of the back face reinforcing member may be
conducted after utilizing the above thermocompression bonding or it may be
independently conducted after the above thermocompression bonding.
Alternatively, a sheet composed of a filler resin material for the front
surface side filler may be used instead of the front surface side filler
previously formed on the light receiving face of the solar cell element in
the above procedures. In this case, the sheet is interposed between the
front surface protective film and the solar cell element to obtain a
composite, and the resultant composite is subjected to thermocompression
bonding, whereby a desirable solar cell module can be obtained.
The thermocompression bonding can include vacuum lamination and roll
lamination.
In the following, the present invention will be described in more detail
with reference to examples which are not intended to restrict the scope of
the present invention.
EXAMPLE 1
1. Preparation of photoelectric conversion element (solar cell)
There were prepared a plurality of solar cells each having the
configuration shown in FIG. 3 and which had a semiconductor active layer
composed of an amorphous silicon (a-Si) material (this solar cell will be
hereinafter referred to as a-Si solar cell) in the following manner.
That is, there was firstly provided a well-cleaned stainless steel plate as
the substrate 301. On the substrate 301, there was formed a two-layered
back reflecting layer 302 comprising a 500 nm thick A1 film and a 500 nm
thick ZnO film by means of a conventional sputtering process, followed by
forming, on the back reflecting layer 302, a tandem type a-Si
photoelectric conversion semiconductor layer 303 with an nip/nip structure
comprising a 15 nm thick n-type layer/a 400 nm thick i-type layer/a 10 nm
thick p-type layer/a 10 nm thick n-type layer/a 80 nm thick i-type layer/a
10 nm thick p-type layer being laminated in the named order from the
substrate side by means of a conventional plasma CVD manner, wherein an
n-type a-Si film as each n-type layer was formed from a mixture of
SiH.sub.4 gas, PH.sub.3 gas, and H.sub.2 gas; an i-type a-Si film as each
i-type layer was formed from a mixture of SiH.sub.4 gas and H.sub.2 gas;
and a p-type .mu.c-Si film as each p-type layer was formed from a mixture
of SiH.sub.4 gas, BF.sub.3 gas, and H.sub.2 gas. Then, on the
semiconductor active layer 303, there was formed a 70 nm thick transparent
and conductive layer 304 composed of In.sub.2 O.sub.3 by means of the
conventional heat resistance evaporation process wherein an In-source was
evaporated in an O.sub.2 atmosphere. Thus, there was obtained a
photovoltaic element.
The resultant photovoltaic element was found to have a shunt resistance of
1 k.OMEGA..cm.sup.2 to 10 k.OMEGA..cm.sup.2. Therefore, the photovoltaic
element was subjected to defect-repairing treatment in the following
manner. That is, the photovoltaic element and an electrode plate were
immersed in an aqueous solution of aluminum chloride adjusted to have an
electric conductivity of 50 to 70 mS such that the electrode plate was
opposed to the transparent and conductive layer of the photovoltaic
element, and wherein the photovoltaic element was electrically grounded.
Then, a positive electric potential of 3.5 V was impressed on the
electrode plate for 2 seconds, whereby the transparent and conductive
layer situated at shunted (or short-circuited) portions in the
photovoltaic element was selectively decomposed. The photovoltaic element
thus repaired was found to have a shunt resistance of 50 k.OMEGA..cm.sup.2
to 200 k.OMEGA..cm.sup.2.
Successively, a grid electrode as the collecting electrode 305 was formed
on the transparent and conductive layer 304 in the following manner. That
is, on the transparent and conductive layer, there was formed a Cu-paste
line with a width of 200 um by means of screen printing. Then, a copper
wire of 100 um diameter was wired on and along the Cu-paste line, a cream
solder was disposed thereon, followed by fusing the solder to thereby fix
the copper wire onto the Cu-paste. A grid electrode was thus formed on the
transparent and conductive layer.
As for the resultant, a copper tab as the negative side power output
terminal 306b was fixed to the substrate 301 using a stainless solder, and
a tin foil tape as the positive side power output terminal 306a was fixed
to the grid electrode as the collecting electrode 305 using solder. Thus,
there was obtained an a-Si solar cell. In this way, there were obtained a
plurality of a-Si solar cells.
2. Preparation of module
Using each of the a-Si solar cells obtained above, there were prepared in
the following manner a plurality of solar cell modules each having the
configuration shown in FIG. 4.
In FIG. 4, reference numeral 401 indicates a photoelectric conversion
element (corresponding to the foregoing a-Si solar cell in this case),
reference numeral 402 a transparent resin thin film layer disposed on the
photoelectric conversion element 401 so as to cover the light receiving
surface thereof, reference numeral 403 a filler (comprising a transparent
organic high-molecular resin layer) which encloses a laminate of the
photoelectric conversion element 401 and the transparent resin thin film
layer 402, reference numeral 404 a front surface protective film disposed
on the filler 403, reference numeral 405 a back face protective film
disposed under the filler 403, and reference numeral 406 a back face
reinforcing member disposed under the back face protective film. The
filler 403 includes a front surface side filler and a backside filler.
(1) Preparation of a laminate comprising a transparent thin film layer 402
formed on a photoelectric conversion element 401 (that is, the a-Si solar
cell obtained in the above) so as to cover the light receiving face:
100 parts by weight of a resin mixture composed of an acrylic resin, an
inorganic polymer, and hexamethylenediisocyanate blocked by
.epsilon.-caplolactam and 2.8 parts by weight of
.gamma.-methacryloxypropyltrimethoxysilane as a silane coupling agent to
obtain a mixture. The mixture was applied onto the light receiving face of
the a-Si solar cell by means of the conventional coating process to form a
coating film, followed by subjecting the coating film to heat treatment to
vaporize the solvent while crosslinking the resin of the coating film, to
thereby form a transparent resin thin film as the transparent resin thin
film layer 402 on the a-Si solar cell 401 so as to cover the light
receiving face thereof. By this, there was obtained a laminate comprising
the a-Si solar cell and the transparent thin film layer.
(2) Provision of a filler material as the filler 403:
(a) As the front surface side filler, there was provided a 460 .mu.m thick
EVA sheet obtained by mixing 100 parts by weight of EVA (ethylene-vinyl
acetate copolymer), 3 parts by weight of
2,5-dimethyl-2,5-bis(t-butylperoxy)hexane as a crosslinking agent, 1.0
part by weight of .gamma.-methacryloxypropyltrimethoxysilane as a silane
coupling agent, 0.3 part by weight of 2-hydroxy-4-n-octoxybenzophenone as
a UV absorber, 0.1 part by weight of
bis(2,2,6,6-tetramethyl-4piperidyl)sebacate as a light stabilizer, and 0.2
part by weight of tris(mono-nonylphenyl)phosphate as an antioxidant to
obtain a mixture, heating the mixture to obtain a fused product, and
subjecting the fused product to extrusion molding using a T-die wherein
the fused product was extruded through the slit of the T-die.
(b) As a backside filler, there was provided a 460 .mu.m thick EVA film.
(3) Provision of a film as the front surface protective film 404:
As the surface protective film 404, there was provided a 38 um thick
stretched ETFE film having a surface which is to be contacted with the
surface of the filler 403 treated by way of corona discharging (the front
surface side filler).
(4) Provision of a film as the back face protective film 405:
As the back face protective film 405, there was provided a laminated film
comprising an EEA (ethylene-ethyl acrylate copolymer) film of 200 um in
thickness/a polyethylene film of 25 um in thickness/a PET (polyethylene
terephthalate) film of 50 um in thickness/an EEA (ethylene-ethyl acrylate
copolymer) film of 200 um in thickness.
(5) Provision of the back face reinforcing member 406:
As the back face reinforcing member 406, there was provided a 0.3 mm thick
galvalume steel member (or a Zn-coated steel member).
(6) Preparation of a solar cell module:
On the light receiving face of the laminate (that is, on the surface of the
transparent resin thin film layer 402 disposed on the a-Si solar cell)
obtained in the above (1), there were laminated the EVA sheet (obtained in
the above (2)-(a)) and the ETFE film (provided in the above (3)) in the
named order. In this case, the corona-discharged surface of the ETFE film
contacted the surface of the EVA sheet. On the rear face of the resultant,
there were laminated the EVA film (provided in the above (2)-(b)), the
laminated film (provided in the above (4)) and the galvalume steel member
(provided in the above (5)) in the named order. Thus, there was obtained a
stacked body. The stacked body thus obtained was placed in a vacuum
laminator, wherein it was subjected to heat treatment at 150.degree. C.
for 30 minutes while evacuating the inside of the vacuum vessel to a
predetermined vacuum, followed by cooling to room temperature. Thus, there
was obtained a solar cell module.
In this way, there were prepared a plurality of solar cell modules.
Evaluation
Using the resultant solar cell modules, evaluation was conducted with
respect to combustibility, heat resistance, adhesion, endurance against
changes in environmental temperature, weatherability, electrical
insulation, and resistance to scratching.
The obtained evaluation results are collectively shown in Table 1.
The evaluation of each of the above evaluation items was conducted in the
following manner:
(1) Evaluation of the combustibility:
The solar cell module was placed on a deck slanted at 22.degree. against
the horizon. A gas burner flame of 760.+-.28.degree. C. was supplied to
the surface covering material side of the solar cell module for 10
minutes, and the flame spreading was observed. The observed results are
shown in Table 1 based on the following criteria:
.largecircle.: the flame spreading is less than 6 feet from the tip, and
X: the flame spreading is beyond 6 feet from the tip.
(2) Evaluation of the heat resistance:
The solar cell module was exposed to an atmosphere of 150.degree. C. for 15
hours, and thereafter, change in the initial transmittance of its surface
covering material of light of 400 nm wavelength was observed. The observed
results are shown in Table 1 based on the following criteria:
.largecircle.: a case where no yellowing occurred (the change in the
initial transmittance is less than 10%), and
X: a case where yellowing occurred (the change in the initial transmittance
is greater than 10%).
(3) Evaluation of the adhesion:
As for the solar cell module, in accordance with JIS K5400 8.5.2, the
adhesion between the transparent resin thin film layer and the transparent
and conductive layer was examined. The observed results are shown in Table
1 based on the following criteria:
.largecircle.: no separation occurred, and
X: separation occurred.
(4) Evaluation of the endurance against changes in environmental
temperature:
The solar cell module was subjected to 20 repetitions of a cycle of
exposure to an atmosphere of -40.degree. C. for an hour and exposure to an
atmosphere of 85.degree. C./85% RH for an hour, and thereafter, its
exterior appearance was optically observed. The observed results are shown
in Table 1 based on the following criteria:
.circleincircle.: no change is observed in the exterior appearance,
.largecircle.: slight change is observed in the exterior appearance but it
is not problematic in practice, and
X: problematic, discernible removal and/or cracking and coloring which are
not acceptable in practice are observed in the exterior appearance.
(5) Evaluation of the weatherability:
The solar cell module was placed in a carbon-arc sunshine weather meter,
wherein it was irradiated with pseudo sunlight for 5000 hours under
conditions of repeating a cycle of maintaining at a black panel
temperature of 63.degree. C. for 108 minutes and a pure water fall for 12
minutes. Thereafter, its exterior appearance was optically observed. The
observed result is shown in Table 1 based on the following criteria:
.circleincircle.: no change is observed in the exterior appearance,
.largecircle.: a slight change is observed in the exterior appearance but
it is not problematic in practice, and
X: problematic, discernible removal and/or cracking and coloring which are
not acceptable in practice are observed in the exterior appearance.
(6) Evaluation of the electrical insulation:
The positive and negative output terminals of the solar cell module were
intentionally short-circuited. A high-potential tester was electrically
connected between the short-circuited terminal and the back face
reinforcing member and 2200 DC voltage was impressed, wherein the leakage
current was measured. The measured results are shown in Table 1 based on
the following criteria:
.largecircle.: the leakage current to 50 .mu.A or less (acceptable), and
X: the leakage current is above 50 .mu.A (not acceptable).
(7) Evaluation of the scratch resistance:
This evaluation was conducted in the following manner. That is, the solar
cell module was subjected to surface treatment in a manner shown in FIG.
5, wherein a 1 mm thick metal plate 602 is contacted via a corner thereof
to the most recessed portion of the light receiving surface side 601 of
the solar cell module. Then, a load F of 2 pounds is applied to the metal
plate and a load F of 5 pounds is applied without moving the metal plate.
Then the metal plate is pulled in a direction indicated by an arrow P
while applying the latter load thereto to form a scratch. Then the solar
cell module thus treated is evaluated for whether or not the scratched
portion of the surface covering material still provides electrical
isolation from the outside. This evaluation is conducted by immersing the
treated solar cell module in an electrolytic solution of 3000 .OMEGA.cm,
and applying a voltage of 2200 V between the photovoltaic element of the
solar cell module and the electrolytic solution and measuring the leakage
current. The observed results are shown in Table 1 based on the following
criteria,:
.largecircle.: the leakage current is 50 .mu.A or less (acceptable), and
X : the leakage current is above 50 .mu.A (not acceptable).
EXAMPLE 2
The procedures of Example 1 were repeated, except that the isocyanate
monomer used in the formation of the transparent resin thin film layer in
Example 1 was replaced by 1,3-bis(isocyanatomethyl)cyclohexane.
Using the resultant solar cell modules, evaluation was conducted in the
same manner as in Example 1.
The results obtained are collectively shown in Table 1.
EXAMPLE 3
The procedures of Example 1 were repeated, except that the EVA used as the
front surface side filler in Example 1 was replaced by EEA (ethylene-ethyl
acrylate copolymer).
Using the resultant solar cell modules, evaluation was conducted in the
same manner as in Example 1.
The results obtained are collectively shown in Table 1.
EXAMPLE 4
The procedures of Example 1 were repeated, except that the silane coupling
agent used in the formation of the transparent resin thin film layer in
Example 1 was replaced by .gamma.-methacryloxypropyltrimethoxysilane.
Using the resultant solar cell modules, evaluation was conducted in the
same manner as in Example 1.
The results obtained are collectively shown in Table 1.
EXAMPLE 5
The procedures of Example 1 were repeated, except that the
.epsilon.-caprolactam used as the blocking agent for the isocyanate
monomer in the formation of the transparent resin thin film layer in
Example 1 was replaced by methyl ethyl ketone oxime.
Using the resultant solar cell modules, evaluation was conducted in the
same manner as in Example 1.
The results obtained are collectively shown in Table 1.
EXAMPLE 6
The procedures of Example 1 were repeated, except that the silane coupling
agent used in the formation of the transparent resin thin film layer in
Example 1 was replaced by .gamma.-glycidoxypropyltrimethoxysilane.
Using the resultant solar cell modules, evaluation was conducted in the
same manner as in Example 1.
The results obtained are collectively shown in Table 1.
EXAMPLE 7
The procedures of Example 1 were repeated, except that fine particles of
silicon oxide having a mean particle size of 10 .mu.m were additionally
used in the formation of the transparent resin thin film layer in Example
1.
Using the resultant solar cell modules, evaluation was conducted in the
same manner as in Example 1.
The results obtained are collectively shown in Table 1.
Comparative Example 1
The procedures of Example 1 were repeated, except that no silane coupling
agent was used in the formation of the transparent resin thin film layer
in Example 1.
Using the resultant solar cell modules, evaluation was conducted in the
same manner as in Example 1.
The results obtained are collectively shown in Table 1.
Comparative Example 2
The procedures of Example 1 were repeated, except that the transparent thin
film layer used in Example 1 was replaced by a 460 .mu.m thick EVA film.
Using the resultant solar cell modules, evaluation was conducted in the
same manner as in Example 1.
The results obtained are collectively shown in Table 1.
Comparative Example 3
The procedures of Example 1 were repeated, except that the transparent thin
film layer used in Example 1 was not used.
Using the resultant solar cell modules, evaluation was conducted in the
same manner as in Example 1.
The results obtained are collectively shown in Table 1.
TABLE 1
______________________________________
endurance
against
changes in elec- resis-
environ- trical tance
com- heat ad- mental weath- insu- to
busti- resis- he- temper- er la- scratch-
bility tance sion ature ability tion ing
______________________________________
Example 1
.largecircle.
.largecircle.
.largecircle.
.circleincircle.
.circleincircle.
.largecircle.
.largecircle.
acrylic/inorg.
polymer
Example 2 .largecircle. .largecircle. .largecircle. .circleincircle.
.circleincircle. .largecircle
. .largecircle.
acrylic/inorg.
polymer
Example 3 .largecircle. .largecircle. .largecircle. .circleincircle.
.circleincircle. .largecircle
. .largecircle.
acrylic/inorg.
polymer
Example 4 .largecircle. .largecircle. .largecircle. .largecircle.
.circleincircle. .largecircle
. .largecircle.
acrylic/inorg.
polymer
Example 5 .largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle.
.largecircle.
acrylic/inorg.
polymer
Example 6 .largecircle. .largecircle. .largecircle. .largecircle.
.largecircle. .largecircle.
.largecircle.
acrylic/inorg.
polymer
Example 7 .largecircle. .largecircle. .largecircle. .largecircle.
.circleincircle. .largecircle
. .circleincircle.
acrylic/inorg.
polymer
Comparative .largecircle. X X X X X X
Example 1
Comparative X X -- .largecircle. .largecircle. .largecircle. .largecircl
e.
Example 2
Comparative .largecircle. .largecircle. -- .largecircle. .largecircle.
X X
Example 3
______________________________________
Based on the results shown in Table 1, the following facts are understood.
That is, by using a specific transparent resin film layer containing a
silane coupling agent, particularly, an epoxy series silane coupling agent
and diminishing the amount of EVA used, there can be attained a highly
reliable surface covering material for a semiconductor element
(specifically, a photoelectric conversion element), in which said
transparent resin thin film layer always secures a sufficient adhesion
with not only the transparent electrode of the semiconductor element but
also the transparent organic resin layer situated above the transparent
resin thin film layer even under environmental conditions with a high
temperature and which is always maintained in a desirable state without
being yellowed even upon repeated used under severe environmental
conditions with a high temperature and a high humidity.
As for a surface covering material having a transparent resin thin film
layer formed using .epsilon.-caprolactam but using no epoxy series silane
coupling agent, it is liable to yellow upon repeated use under
environmental condition with a high temperature. As for the reason for
this, it is considered that EVA contained in the surface covering material
liberates acetic acid when it is oxidized and deteriorated and the acetic
acid thus liberated reacts with .epsilon.-caprolactam remaining in the
transparent resin thin film layer to yellow the surface covering material.
However, the incorporation of the epoxy series silane coupling agent into
the transparent resin thin film layer eliminates the occurrence of the
yellowing problem. That is, the epoxy series silane coupling agent
functions to trap the liberated acetic acid, whereby the yellowing problem
is effectively prevented from occurring.
Further, even in the case where EEA is used instead of EVA, no acid
generation occurs in acid decomposition reaction of the EEA. This also
prevents the surface covering material from being yellowed. However, in
the case of using methyl ethyl ketone oxime (that is, MEK oxime), although
yellowing of the surface covering material can be prevented, there is a
drawback such that during the process of forming a coating film by way of
heat treatment, the MEK oxime decomposes to produce a highly reactive
nitrogen compound and because of this, the probability of yellowing of the
surface covering material is greater than that in the case of using
.epsilon.-caprolactam and upon repeated use over a long period of time,
the surface covering material is liable to yellow.
Further, as is apparent from the evaluation results obtained in the
endurance test against changes in environmental temperature and the
environment resistance tests including the weatherability test, it is
understood that each of the solar cell modules obtained in the examples
belonging to the present invention is free of the occurrence of layer
separation in the stacked body and maintains its original exterior
appearance without being damaged. In addition, as for the electrical
insulation, each of the solar cell modules obtained in the examples
belonging to the present invention has an excellent initial state in terms
of exterior electrical insulation and even after various endurance tests,
still maintains a satisfactory electrical insulation state.
Hence, it is understood that each of the solar cell modules obtained in the
examples belonging to the present invention excels in module
characteristics and can be safely repeatedly used over a long period of
time and therefore, is highly reliable.
As is apparent from the above description, according to the present
invention, in a semiconductor device such as a solar cell module in which
at least the incident light side surface of a semiconductor element is
sealed by a transparent resin layer and at least a transparent organic
high-molecular resin layer, by incorporating into the transparent resin
layer a silane coupling agent, particularly, a compound represented by the
general formula XSiY.sub.3 with X being a reactive organic functional
group and Y being a hydrolyzable group, there can be attained a highly
reliable surface covering material which is hardly deformed and hardly
peeled and excels in heat resistance even upon repeated use under such
severe environmental conditions that the solar cell module is heated to a
high temperature with repeated irradiation of direct sunlight in the
outdoors. In addition, there can be attained a highly reliable surface
covering material for a solar cell module which is hardly yellowed and
excels in heat resistance and which therefore effectively maintains the
solar cell characteristics in a desirable state without being deteriorated
even upon repeated use under severe environmental conditions with a high
temperature and a high humidity.
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